You say "is the EMD F7B HO..." That depends on which one you're looking at -- a for sale listing should say what scale somewhere. Unless you're asking if they are AVAILABLE in HO, and the answer is yes, although I'm not sure anyone is making new models of one at the moment.
Thing is, as CV said, the B unit is intended to help pull a train while the engineer rides in the accompanying "A" unit. Unless the model you're looking at is a dummy, it is a real loco and will pull a train... but it will look funny doing so by itself.
In the picture below, the lower loco is the B unit:
(Image credit www.walthers.com